In a mobile communication system using CDMA (Code Division Multiple Access) which has become increasingly common in recent years, random access is used for one of uplink channels from a mobile station to a base station. For example, in IMT-2000 (DS-CDMA), a PRACH (Physical Random Access Channel) corresponds thereto. Channel models and communication protocols of the PRACHs, which are described in documents such as 3GPP TS25.211, etc., use preamble signals as signals for,conveying message signal transmission permission request from a mobile unit to a base station, and message signals for transmitting information from an actual mobile unit.
Here, it is throughput that is important in transmitting/receiving PRACHs which are first transmitted when a mobile unit is powered on, and when calling as well as when packet data is transmitted. This is because poor PRACH throughput causes the user to feel inconvenienced by ‘not readily getting through’. The simplest way to enhance this throughput is to increase the number of simultaneous decoding, i.e., the number of allowable simultaneous decoding of PRACH message signals in a base station, as an alternative to reducing signal errors to reduce the number of times of retransmission.
To increase the number of simultaneous decoding, however, from the point of view of device scale and cost, it is not very well advisable to simply increase the number of a path detection correlator set as in FIG. 1 and RAKE receivers as in FIG. 2. The correlator set is used not only for message signal path detection, but also for preamble signal detection. In detecting message signal paths, a delay profile is selectively obtained in the vicinity of a delay amount in which are received preamble signals, whereas, in detecting preamble signals, because of no such preliminary information, the use of a correlator set to obtain a delay profile is required for all of up to a maximum delay amount matched to a cell radius. Therefore, as the cell radius is larger as in FIG. 3, more correlator sets are required for preamble signal detection, while the number of correlator sets that can be used for message signal path detection is limited. As a result, the number of RAKE receivers that can be operative in the decoder is also decreased.
Accordingly, it is an object of the present invention to provide a path diversity reception device and method for a spread spectrum communication system with improved throughput by efficiently using a signal-processing portion of the path diversity reception device when implementing random access using preamble signals in the spread spectrum communication system such as a CDMA system, etc., used in mobile communications, etc.